Humidity Calibator

8/3/2019 Humidity Calibator

1/23

Humidity CalibratorHMK15

USER'SGUIDEM210185en-B

September 2002


2/23

M210185en-A User's Guide

ii


3/23


iii

PUBLISHED BY

Vaisala OyjPhone (int.): (+358 9) 894 91

P.O. Box 26 Fax: (+358 9) 8949 2227FIN-00421 Helsinki

Finland

Visit our Internet pages at http://www.vaisala.com/

Vaisala 2002

No part of this manual may be reproduced in any form or by any

means, electronic or mechanical (including photocopying), nor may its

contents be communicated to a third party without prior written

permission of the copyright holder.

The contents are subject to change without prior notice.
http://www.vaisala.com/http://www.vaisala.com/


4/23


iv

Contents

1. PRODUCT DESCRIPTION................................................................................................... 1

1.1. General .................................................................................................................... 1

1.2. Calibration certificate of the salt packages........................................................... 2

2. PREPARING THE SALT SOLUTIONS ................................................................................. 2

2.1. General instructions ............................................................................................... 2

2.2. Preparing the solutions .......................................................................................... 3

3. INSTRUCTIONS FOR THE CALIBRATION OF HUMIDITY INSTRUMENTS ....................... 7

3.1. General instructions ............................................................................................... 7

3.1.1. Thermometer............................................................................................. 8

3.2. Calibration............................................................................................................... 9

3.3. Greenspan's calibration table1............................................................................ 11

3.4. On-site calibrations and transportation............................................................... 11

4. MAINTENANCE ................................................................................................................. 15

5. SPARE PARTS AND ACCESSORIES ................................................................................ 15

6. TECHNICAL DATA ............................................................................................................ 16

WARRANTY


5/23


v

This page intentionally left blank.


6/23


7/23

1. PRODUCT DESCRIPTION

1.1. General

The HMK15 humidity calibrator has been developed for calibration and checking

of humidity probes and transmitters. The functioning of the calibrator is based on

the fact that certain salt solutions generate a certain relative humidity in the air

above them.

The four holes in the chamber cover are designed for Vaisala probes and

transmitters with 12 mm, 13.5 mm (2 holes) and 18.5 mm diameters. The saltsolutions suitable for the HMK15 calibrator are e.g. lithium chloride LiCl

(11 %RH), magnesium chloride MgCl2 (33 %RH), sodium chloride NaCl(75 %RH) and potassium sulphate K

2SO

4(97 %RH). In calibration, the sensor

head is inserted into a salt chamber containing a saturated salt solution. The

probe/transmitter reading is then adjusted to the correct value, i.e. to the

humidity that the specific salt solution generates at that particular temperature.

Calibration is usually performed at least at two different humidities to ensure

the sensor accuracy over the entire humidity range (0 - 100 %RH).

The HMK15 calibrator is suitable for both laboratory and field usage. During

transportation, the chambers can be tightly closed with specially designed

transit covers. The optional transit bag (order code HM27032) helps to

transport the calibrator in the vertical position. Furthermore, the bag can be

used for housing the calibrator also during calibration.

The following photo shows the HMK15 calibrator with some accessories

(marked with *):

Figure 1.1 The HMK15 calibrator with some accessories (*)

Salt chamber

Thermometer

Adapter fitting

Plugs

*Ready dosed

salt packagewith calibrationcertificate

Calibration

certificate forthermometer

*Ion exchanged water

Measurement cup

Mixing spoon

Base plate


8/23

User's Guide M210185en-B

2

Accessories include additional salt chambers, ion exchanged water, transit bag and

ready-dosed salt packages (LiCl 11%RH, MgCl2 33 %RH, NaCl 75 %RH,

K2SO4 97 %RH).

1.2. Calibration certificate of the salt packages

Vaisala's ready-dosed salt packages are delivered with calibration certificates

given on the basis of a batch check. In other words, a sample of packages are

taken from a batch and salts are prepared according to the instructions given in

this manual. These salt solutions are then checked at Vaisala Oy's

Measurement Standards Laboratory (this calibration laboratory is accredited

by FINAS, a member of the European Cooperation for Accreditation of

Laboratories). The calibration certificate certifies that the equilibrium

humidities generated by these salt solutions correspond to Greenspan's

calibration table within the specified accuracy (see Chapter6).

2. PREPARING THE SALT SOLUTIONS

2.1. General instructions

Prepare the salts using the equipment provided with the calibrator or

make sure that all accessories used are suitable for preparing salt

solutions and are absolutely clean. If necessary, wash them carefully

and rinse several times before preparing the salt solutions. The last

rinse must be made with distilled or ion exchanged water.

The salts are quick and easy to prepare with Vaisala's ready-dosed salt

packages. If you do not use ready-dosed salt packages, measure the

salts using the measurement cup provided. Make sure that the cup is

clean before measuring the salts. In the following instructions, the

required amounts are given in grammes and millilitres. The salt

solutions must be prepared from salts of pro analysis grade; these are

available in agencies selling industrial chemicals. Note that the water

must be distilled or ion exchanged (conductivity < 0.25 S/cm). Ion

exchanged water can also be ordered as an accessory for the HMK15

calibrator (order code 19767HM).

Handle the salts and equipment carefully and keep them absolutely

clean so that the salts are not contaminated. Make sure that the salts

do not mix.

At the bottom of the salt chamber there must not be more than 1 cm

of undissolved salt and liquid. Otherwise, the sensor to be calibrated

can be immersed into the solution. If necessary, verify the amount e.g.

with the measurement spoon.

Various standards (ASTM E104-85, DIN 50008, JIS Z8806) include

recommendations and instructions on how to prepare and store salt

solutions.


9/23


3

2.2. Preparing the solutions

Lithium chloride generates a reference humidity of approximately 11 %RH.

It is normally used as the dry end (offset) reference.

NOTE

Never add water to dry LiCl salt; the salt may heat up

so rapidly that it splashes out of the chamber.

NOTE

LiCl is harmful when swallowed; the solution is also

corrosive.

NOTE

If the LiCl solution is used or stored in temperatures

below +18C, its equilibrium humidity changes

permanently.

Magnesium chloride generates a reference humidity of approximately33 %RH. It is often used as a check point if calibration is performed at more

than two points.

Sodium chloride generates a reference humidity of approximately 75 %RH. It

is used as the wet end reference (gain) for probes measuring in applications

with normal humidities.

Potassium sulphate generates a reference humidity of approximately

97 %RH. Potassium sulphate is used as the wet end reference (gain) for probes

measuring in applications with very high humidities (90 - 100 %RH, e.g.

outdoor and concrete measurements).

Prepare the salt solutions according to the following instructions. Measure the

salts carefully if you do not use the ready-dosed packages.


10/23


4

1. Take the calibrator out of the box. Open the transit cover of the

chamber. Remove the measurement cover from the chamber holder

and press the transit cover on the holder (see Figure 2.1).

Figure 2.1 Press the transit cover on a chamber holder

2. Pour ion exchanged water into the chamber; the required amounts are

given in the table:

LiCl 12 ml of water

MgCl2 3 ml of water

NaCl 10 ml of water

K2SO4 10 ml of water

Figure 2.2 Pour a correct dose of ion exchanged water into the

chamber; dry the measurement cup

2. Sprinkle the contents of a salt package (or measure the salt according

to the table) in small quantities into the chamber, stirring constantly.

When measuring with the measurement cup, make sure that the cup is

clean and dry. Rinse and dry the cup after every use.


11/23


5

LiCl 15 g or 18 ml

MgCl2 30 g or 30 ml

NaCl 20 g or 15 mlK2SO4 30 g or 20 ml

Figure 2.3 Sprinkle a correct dose of salt into the chamber

stirring constantly

4. When all salt has been sprinkled into the chamber, the saturated salt

solution should have the ratio of 60 - 90 % undissolved salt to10 - 40 % liquid.

5. Close the chamber with the chamber cover (Figure 2.4).

Figure 2.4 Close the chamber with the chamber cover


12/23


6

6. Fasten the salt chamber on the holder in the base plate and close the

measurement holes with rubber plugs. The chambers can also be used

as individual checkers without the base plate. NOTE: the plugs have

three steps, each of which is suitable for a certain hole diameter: the

first step for the 12 mm, the second step for the 13.5 mm and the thirdstep for the 18.5 mm hole. Keep the holes always closed when not

calibrating.

7. Write the preparation date on a sticker and mark the chamber with it.

If you use a ready-dosed salt package, use the sticker with the batch

code. Mark all parts of the salt chamber (chamber, chamber cover and

transit cover) with stickers. This way, various covers and different

salts do not get mixed.

Figure 2.5 Mark the chamber and covers with stickers

8. Allow approximately 24 hours for stabilization before use so that the

salt solution reaches the equilibrium humidity.

9. See Chapter4 on how to maintain the salt solutions.

NOTE

If you do not use the instrument for a longer period of

time, close the chambers with transit covers.


13/23


7

3. INSTRUCTIONS FOR THE CALIBRATION OF HUMIDITY

INSTRUMENTS

3.1. General instructions

Usually, the errors during humidity calibration are due to temperature

differences. A temperature difference of 1C at +20C between the air in the

chamber and the sensor causes an error of 3 %RH at 50 %RH and an error of

6 %RH at 97 %RH. The more the transportation or process temperatures

differ from the temperature at the calibration site, the longer the stabilization

time required. In laboratory use, the calibrator should be stored in that part of

the room where the temperature is most stable. The calibrator must be kept out

of direct sunlight and away from localized heat sources, such as spot lights,

heaters and soldering irons. If the probe/transmitter is checked against several

humidity references, the checking must first be made at the dry end. Moredetailed instructions are given in individual manuals of transmitters and

probes.

Handle the probe as little as possible. Do not hold the salt chamber or other

parts of the calibrator in hand during calibration as they warm up and cause

errors in the readings.

NOTE: even the smallest water drop on the probe near the sensors distorts the

readings. Make sure that chamber covers and plugs are carefully closed.

0 0

1 0

2 0

3 0

4 0

5 0

C

HMP233probe

O-rings

sensors

max.1 cm

thermometer

saturated salsolution

undissolvedsalt

Figure 3.1 Salt chamber


14/23


8

3.1.1. Thermometer

The calibrator includes a thermometer which can contain either mercury or red

capillary liquid. If the thermometer contains mercury, it is delivered with a

calibration certificate. The accuracy of the mercury thermometer is sufficientfor checking the transmitter's temperature channel if desired. The mercury

thermometer has been calibrated at five points and the result is traceable to the

Measurement Standards Laboratory of the Centre for Metrology and

Accreditation in Finland. For more accurate results, use the corrections given

in the calibration certificate or their interpolated values. Consider also the

parallax error which may occur while reading the results. The mercury

thermometer should be recalibrated within three years in order to maintain the

traceability.

The manufacturer of the thermometer with red capillary liquid provides it with

a factory calibration certificate. As the accuracy and stability of this kind of athermometer are inferior to those of a mercury thermometer, it is not

recommended to be used for checking the temperature channel of the

transmitter.

The sleeve at the end of the thermometer's protective tube can be used in two

different positions. The thermometer is delivered with the sleeve in such a

position that it protects the part containing the capillary liquid. When turned

the other way round, it acts as an adapter when the thermometer is inserted

into the 13.5 mm hole (see Figure 3.2).

Figure 3.2 The sleeve protects the part with capillary liquid (on the

left) or acts as an adapter (on the right)

During calibration, the thermometer is inserted into the 13.5 mm hole of a salt

chamber. Press it downwards until it passes the O-rings. The thermometer is

correctly in place when you can feel a resistance while pressing it downwards.


15/23


9

Figure 3.3 During calibration, the thermometer is inserted into the

13.5 mm hole

When the thermometer is not in use or the calibrator is transferred from one

place to another, place the thermometer in holders (Figure 3.4).

Figure 3.4 Place the thermometer in holders when not in use

3.2. Calibration

Perform the calibration according to the following instructions:

Leave the HMK15 calibrator and the probe at the calibration site for

at least 30 minutes before starting the calibration in order to let the

probe temperature stabilize to the room temperature.

With lithium chloride it is not necessary to use the thermometer as the

humidity reading changes only very slightly in the temperature range

of +25...+30 C. However, if you use it make sure that the sleeve is in

the correct position and insert it into the 13.5 mm hole of the LiCl salt

chamber. NOTE: handle the thermometer as little as possible and do

not handle it by the measuring end. Press the thermometer downwards

until it passes the O-rings. The thermometer is correctly in place when

you feel a resistance while pressing it downwards.


16/23


10

Take off the grid or filter protecting the sensor. Take care not to

damage the sensor.

Some 12 mm probes need a adapter fitting to fit into the 13,5 mm

hole. Adapter fitting prevents sensor from soaking in the salt liquid.In case you need an adapter fitting, take off the grid or filter and

replace it with the adapter fitting. Two adapter fittings are attached on

the base plate of the HMK15, see picture on page 1.

CAUTION Remember to check from the user's guide of your device if theadapter fitting is needed. If sensor accidently soaks in salt liquid,

remove it quickly and rinse with clean water. Let it dry before taking

into use again.

Insert the probe into a suitable hole of the LiCl salt chamber. Press it

downwards until it passes the O-rings. The shorter the time the hole

stays open before inserting the probe, the shorter the stabilization time

required.

Wait until the humidity reading stabilizes; this takes about 10 - 30

minutes.

Read the salt chamber temperature from the thermometer and then

read the closest humidity value from the calibration table

(Greenspan's calibration table, LiCl solution).

Adjust the dry end (DRY, offset) to correspond to the value given in

the calibration table.

Insert the thermometer into the 13.5 mm hole of the NaCl salt

chamber. NOTE: when calibrating probes that are being used for long

term measurements (over 1 hour) in high humidities (90 - 100 %RH),

use the K2SO4 salt as the high end reference.

Insert the probe into a suitable hole of the NaCl (or K2SO4) salt

chamber. The shorter the time the hole stays open before inserting the

probe, the shorter the stabilization time required.

Wait until the humidity reading stabilizes; this takes about 10 - 30

minutes. Note that in high humidities the risk for errors increases.

Therefore, the stabilization time should be longer (approximately

20 - 40 minutes).

Read the salt chamber temperature from the thermometer and then

read the closest humidity value from the calibration table

(Greenspan's calibration table, NaCl or K2SO4 solution).

Adjust the wet end (WET, gain) to correspond to the value given in

the calibration table.


17/23


11

3.3. Greenspan's calibration table1

C LiCl MgCl2 NaCl K 2SO4

0 * 33.7 0.3 75.5 0.3 98.8 1.1

5 * 33.6 0.3 75.7 0.3 98.5 0.910 * 33.5 0.2 75.7 0.2 98.2 0.8

15 * 33.3 0.2 75.6 0.2 97.9 0.6

20 11.3 0.3 33.1 0.2 75.5 0.1 97.6 0.5

25 11.3 0.3 32.8 0.2 75.3 0.1 97.3 0.5

30 11.3 0.2 32.4 0.1 75.1 0.1 97.0 0.4

35 11.3 0.2 32.1 0.1 74.9 0.1 96.7 0.4

40 11.2 0.2 31.6 0.1 74.7 0.1 96.4 0.4

45 11.2 0.2 31.1 0.1 74.5 0.2 96.1 0.4

50 11.1 0.2 30.5 0.1 74.4 0.2 95.8 0.5

* If the LiCl solution is used or stored in temperatures below +18C, its equilibriumhumidity changes permanently

The numbers on the right in each column indicate the uncertainty of the

reference humidity of the salt in that temperature.

1Greenspan, L.: Journal of Research of the National Bureau of Standards - A

Physis and Chemistry Vol. 81A, No. 1 January-February 1977, pp. 89-95

3.4. On-site calibrations and transportation

The HMK15 calibrator is easily trasferred from one place to another. Two O-

rings seal the transit cover on the chamber. The optional transit bag helps to

transport the calibrator so that chambers stay in the vertical position.

Furthermore, the bag can be used for housing the calibrator during calibration.

When transferring the calibrator from one place to

another, follow the instructions below:

Turn the protective sleeve on the

thermometer and place the

thermometer in the holder.

Replace chamber covers withtransit covers. Press chamber covers

on vacant chamber holders for

transportation.

During transportation, keep the

calibrator so that the chambers stay as

upright as possible. This way, very

little salt solution gets on transit

covers and cleaning is easier. The

closer the transportation temperature is to the temperature of the

calibration site, the shorter the time required for temperaturestabilization. If the transportation temperature is below +18 C, the


18/23


12

LiCl salt chamber should be transported separately to keep the

solution warm.

When the calibrator is at the calibration site, remove transit covers

and fasten chamber covers on salt chambers. Close the holes with

plugs. NOTE: the plugs have three steps each of which is suitable for

a certain hole diameter: the first step for the 12 mm, the second step

for the 13.5 mm and the third step for the 18.5 mm hole.

Clean the transit covers with a damp cloth and press them on vacant

chamber holders.

Take the thermometer off the holder, turn the sleeve the other way

round and perform the calibration according to Chapter3.2.

In on-site calibrations it is important to allow enough time for the calibratorand probe temperatures to stabilize. Depending on the temperature differences

between the transportation and the calibration site or between the probe

removed from the process and the calibration site, a two point calibration

takes about 0.5 - 2 hours. If there are several frequently calibrated instruments

at the same site, knowing the stabilization times is useful.

The following figure illustrates an example of temperature and humidity

stabilization. In this example, an HMP233 probe has been transferred from a

temperature of 75C (oven) to a suitable hole of the NaCl salt chamber; the

calibrator is at room temperature. The figure shows that after 40 minutes, the

humidity reading differs 0.2 %RH from the final reading.

Time [min]

Hum

idity[%RH

70

71

72

73

74

75

76

77

78

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

10

20

30

40

50

60

70

80

90

Temp

erature[C]

HUMIDITY

TEMPERATURE

Figure 3.5 An example of RH and T stabilization when the probe is

removed from a process


19/23


13

Time [min.]

Humidity[%RH

60

62

64

66

68

70

72

74

0 10 20 30 40 50 60 70 80 90 100 110 120

0

4

8

12

16

20

24

28

Temperature[C]

HUMIDITY

TEMPERATURE

Figure 3.6 An example of the RH and T stabilization when the

transportation and calibration site temperatures are

different


20/23


14

In the following example, the transportation temperature of the calibrator

(without the LiCl) is +5C; the calibrator is then transferred into room

temperature. After this, an HMP233 probe that has been stored at room

temperature, is inserted into a suitable hole of the NaCl salt chamber. The

figure shows that after 40 minutes, the reading differs 1.4 %RH from the finalreading.

Time [min.]

Humidity[%RH]

60

62

64

66

68

70

72

74

0 10 20 30 40 50 60 70 80 90 100 110 120

0

4

8

12

16

20

24

28

Tempe

rature[C]

HUMIDITY

TEMPERATURE

Figure 3.7 An example of the RH and T stabilization when the

transportation and calibration site temperatures are

different


21/23


15

4. MAINTENANCE

Depending on the frequency of use and the general operating conditions, the

salt solutions maintain their characteristics for 6 - 12 months. After that, theymust be replaced. A visual check should be performed at intervals of 2 - 3

months. There must be a minimum of approximately 10% of undissolved salt

at the bottom of the chamber (max. 90%) and the salt must be clean, otherwise

it must be reprepared. Please, note that the LiCl solution may crystallize on

the surface. However, there may still be solution under the surface. Therefore,

in such cases stir the solution and check it again the next day. It is advisable to

keep a maintenance log which shows the dates of salt replacements and other

maintenance procedures.

For correct calibration it is essential that salt chambers are tightly closed.

Check the O-rings at each salt replacement. If they are damaged, replace themwith new ones. The O-rings used are of the following types:

O-ring location dimensions type

measurement hole 12 mm 12 x 2.5 mm NBR70

measurement hole 13.5 mm 13.5 x 2.5 mm NBR70

measurement hole 18.5 mm 18.3 x 2.4 mm NBR70

transit cover 41.2 x 3.0 mm NBR70

chamber 50.0 x 2.0 mm NBR70

5. SPARE PARTS AND ACCESSORIES

Order code Description

19728HM Mercury thermometer with calibration certificate

25130HM Thermometer with red capillary liquid

19729HM Ready-dosed LiCl salt package with calibration certificate

19730HM Ready-dosed MgCl2 salt package with calibration certificate

19731HM Ready-dosed NaCl salt package with calibration certificate

19732HM Ready-dosed K 2SO4 salt package with calibration certificate

19746HM Plug set

19766HM Salt chamber

19767HM Ion exchanged water

211011 Adapter fitting for 12 mm probes

HM27032 Transit bag


22/23


16

6. TECHNICAL DATA

Operating temperature range +0 ...+50 C

NOTE

If the LiCl solution is used or stored in

temperatures below +18C, its equilibrium humidity

changes permanently.

Accuracy:

lithium chloride LiCl 1.0 %RH + Greenspan's uncertainty*

magnesium chloride MgCl2 1.0 %RH + Greenspan's uncertainty*

natrium chloride NaCl 1.4 %RH + Greenspan's uncertainty*

potassium sulphate K2SO4 1.5 %RH + Greenspan's uncertainty*

* = The uncertainty given in Greenspan's calibration table (see Chapter 3.3) at the calibration

temperature, e.g. the accuracy of LiCl salt at +20 C is (1.0 + 0.3) %RH = 1.3 %RH

Response time (probe and calibrator

at the same temperature) with Vaisala sensors typically 10 min.

(deviation of the final value < 1%RH)

Accuracy of the thermometer:

with mercury 0.3 C

with red capillary liquid 1 C

Dimensions 20 x 9 x 23 cm

Materials metal parts: anodised aluminium

Weight 1 kg without salt solutions


23/23


Warranty

Vaisala hereby represents and warrants all Products manufactured by Vaisala and sold hereunder to be free from

defects in workmanship or material during a period of twelve (12) months from the date of delivery save for

products for which a special warranty is given. If any Product proves however to be defective in workmanship ormaterial within the period herein provided Vaisala undertakes to the exclusion of any other remedy to repair or at

its own option replace the defective Product or part thereof free of charge and otherwise on the same conditions

as for the original Product or part without extension to original warranty time. Defective parts replaced in

accordance with this clause shall be placed at the disposal of Vaisala.

Vaisala also warrants the quality of all repair and service works performed by its employees to products sold by

it. In case the repair or service works should appear inadequate or faulty and should this cause malfunction or

nonfunction of the product to which the service was performed Vaisala shall at its free option either repair or

have repaired or replace the product in question. The working hours used by employees of Vaisala for such repair

or replacement shall be free of charge to the client. This service warranty shall be valid for a period of six (6)

months from the date the service measures were completed.

This warranty is however subject to following conditions:

a) A substantiated written claim as to any alleged defects shall have been received by Vaisala within thirty (30)

days after the defect or fault became known or occurred, and

b) The allegedly defective Product or part shall, should Vaisala so require, be sent to the works of Vaisala or to

such other place as Vaisala may indicate in writing, freight and insurance prepaid and properly packed and

labelled, unless Vaisala agrees to inspect and repair the Product or replace it on site.

This warranty does not however apply when the defect has been caused through

a) normal wear and tear or accident;

b) misuse or other unsuitable or unauthorized use of the Product or negligence or error in storing, maintaining or

in handling the Product or any equipment thereof;

c) wrong installation or assembly or failure to service the Product or otherwise follow Vaisala's service

instructions including any repairs or installation or assembly or service made by unauthorized personnel not

approved by Vaisala or replacements with parts not manufactured or supplied by Vaisala;

d) modifications or changes of the Product as well as any adding to it without Vaisala's prior authorization;

e) other factors depending on the Customer or a third party.

Notwithstanding the aforesaid Vaisala's liability under this clause shall not apply to any defects arising out of

materials, designs or instructions provided by the Customer.

This warranty is expressly in lieu of and excludes all other conditions, warranties and liabilities, express or

implied, whether under law, statute or otherwise, including without limitation any implied warranties of

merchantability or of fitness for a particular purpose and all other obligations and liabilities of Vaisala or its

representatives with respect to any defect or deficiency applicable to or resulting directly or indirectly from the

Products supplied hereunder, which obligations and liabilities are hereby expressly cancelled and waived.

Vaisala's liability shall under no circumstances exceed the invoice price of any Product for which a warranty

claim is made, nor shall Vaisala in any circumstances be liable for lost profits or other consequential loss whether

direct or indirect or for special damages.

Humidity Calibator

Documents

Transcript of Humidity Calibator